Effects of Gold Tailings Fineness and Dosage on the Rheology and Mechanical Properties of ECC

This study systematically investigates the effects of gold tailings (GT) sand substitution levels and particle fineness on the rheological behavior, mechanical properties, and microstructural characteristics of Engineered Cementitious Composites (ECC). The results demonstrate that incorporating moderate amounts of GT sand (≤75%) effectively enhances both the compressive strength and fracture toughness of the composite. However, complete substitution (100% GT) significantly increases matrix porosity, leading to a consequent reduction in comprehensive mechanical strength. A critical size-dependent decoupling effect was observed: while the full replacement of fine aggregates with coarse GT severely degrades compressive strength due to excessive void formation, it unexpectedly increases the matrix fracture toughness by inducing significant crack deflection and tortuosity. Conversely, the incorporation of fine GT optimizes the distribution of matrix flaws and fosters a stable fiber pull-out mechanism. Consequently, despite a reduced pseudo-strain hardening (PSH) index, the fine GT-blended ECC achieves a remarkable tensile ductility of up to 3.0% by satisfying the fundamental multiple-cracking energy criteria while maximizing frictional energy dissipation. Furthermore, substituting natural silica sand with GT yields a highly sustainable composite, reducing carbon dioxide emissions by 41% and material costs by 20% without compromising core mechanical performance.